The WHO states that precautions should be taken to protect yourself from COVID-19 if you are pregnant, as pregnant people can be badly affected by respiratory disease. At the time of writing, over 51,000 pregnant people in the US have been infected with COVID-19, with 60 deaths recorded. There have even been confirmed cases of babies being infected with the virus while still in the womb. A new study in the journal Cell has reported that the transfer of SARS-CoV-2 antibodies to fetuses via the placenta is low, notably in infections in the third trimester.
Researchers analyzed umbilical cord and blood samples that were collected from pregnancies during the first few months of the pandemic. They compared the parent-fetus transfer of SARS-Cov-2 antibodies to two other respiratory diseases that are able to be vaccinated for, influenza and whooping cough. The levels of antibodies for influenza and whooping cough were higher in the umbilical cord than in the blood. This indicates the efficient transfer of antibodies – and therefore immunity – to the fetus. However, this was not the case for SARS-CoV-2 antibodies. The levels of antibodies specific to the virus were actually lower in the umbilical cord than in the blood, indicating compromised transfer to the fetus.
This reduced antibody transfer may be due to different glycosylation of SARS-CoV-2 antibodies. Glycosylation is where a carbohydrate is added to the Fc region of the antibody, which is the region that communicates with the immune system. The Fc region also binds to the neonatal Fc receptor, which allows the transport of antibodies to the fetus. Antibody glycosylation affects the transfer of antibodies across the placenta, and different types of glycosylation are transferred preferentially. In this study, the glycosylation of antibodies for the SARS-CoV-2 spike protein was shown to be significantly different from normal. This could explain the compromised transfer of antibodies to the fetus.
The findings of this study are not all doom and gloom. For starters, none of the infants born were infected with the virus, and COVID-19 infection did not seem to affect the glycosylation or transfer of antibodies not related to SARS-CoV-2. Reduced antibody transfer was not seen in pregnant people infected in their second trimester, but was seen in those infected in their third trimester. The researchers theorize that this could be due to inflammation-induced changes in glycosylation resolving over time.
This is a scary time for expectant parents. On top of the general stress of being pregnant during a pandemic, there has been scaremongering around the effects of the upcoming vaccines on pregnancy. Results like these, while they may seem disheartening, allow us to better understand the effects of COVID-19 on pregnancy, and better protect those who are expecting.